The present invention relates to ground fault circuit interrupting (GFCI) devices and particularly to an improved integrated circuit ground fault signal processor therefor.
GFCI devices are presently enjoying wide application in certain residential circuits, on construction sites and in industry to protect personnel from potentially injurious electrical shock should they become involved in a line-to-ground fault. Such devices are typically available in either a circuit breaker configuration acceptable in a conventional circuit breaker load center or a receptacle configuration acceptable in a conventional wall outlet box. To achieve their acceptability in such existing facilities, GFCI devices must be dimensionally comparable to conventional circuit breakers and receptacles lacking ground fault protection capability. Consequently, the components operating to afford ground fault protection must be highly miniaturized to accommodate being packaged in very little available space. Thus, the requisite electronics should be implemented in integrated circuit form. Discrete components should be compact in size and as few in number as possible. The cores of the requisite differential current transformer and double grounded neutral transformer must also be quite small.
Since, in both the GFCI breaker and receptacle configurations, the components are typically housed in a molded insulative case, power consumption of the electronic components must be kept low in order to minimize internal temperature rise. As is well understood, heat has a particularly detrimental effect on the reliability, stability and life of electronic elements, whether in discrete or integrated circuit form.
GFCI receptacles have required full-wave rectification of the line current sine wave for the power supply in order to achieve full-wave operation since the phase relationship of the ground fault signal and the signal processor operating power derived from the line current is not fixed, i.e. the line and neutral connections with the distribution circuit can be readily reversed during installation. This cannot be done when installing a GFCI breaker, and thus half-wave rectification is sufficient assuming proper hard wire connectors of the differential transformer secondary winding terminations to the signal processor have been made during manufacture. Consequently, the GFCI modules differ in this respect and are not interchangeable as between circuit breakers and receptacles, a distinct disadvantage from a manufacturing standpoint.
It has been found that detection of, for example, a positive ground fault signal voltage alone can contribute to failure in meeting specified trip-time requirements in the special situation when the GFCI device is closed in on a pre-existing, severe ground fault condition at the beginning of a negative half-cycle of the power supply voltage with the ground fault signal being out of phase with the supply voltage. Under these circumstances, it would be necessary for the signal processor to also respond to a relatively large negative ground fault signal voltage in a manner such that a trip function can be executed within allowable trip time limits.
It is accordingly an object of the present invention to provide an improved ground fault circuit interrupting device.
A further object is to provide a ground fault circuit interrupting device of the above character wherein power consumption of the ground fault signal processor is minimized.
An additional object is to provide a ground fault circuit interrupting device of the above character wherein ground fault signal detection is carried out on a full-cycle basis.
Another object is to provide a ground fault circuit interrupting device of the above character which includes an integrated circuit signal processor capable of application in either a GFCI circuit breaker configuration or a GFCI receptacle configuration.
A further object is to provide a ground fault circuit interrupting device of the above character, which is efficient in construction, convenient to manufacture and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.